We measured the critical nasal pressure (Pcrit), at which the upper airway collapses, in prepubertal children with obstructive sleep apnea syndrome (OSAS) compared to asymptomatic snoring. We found that Pcrit was higher in OSAS patients. Inspiratory airflow varied in proportion to upstream rather than downstream pressure changes. A reduction in Pcrit was associated with clinical improvement. We conclude that airway collapsibility is higher in children with OSAS than with snoring.